Immunostaining and in situ DNA analysis are useful tools in histological diagnosis and the study of tissue morphology. Immunostaining relies on the specific binding affinity of antibodies with epitopes in tissue samples, and the increasing availability of antibodies which bind specifically with unique epitopes present only in certain types of diseased cellular tissue. Immunostaining requires a series of treatment steps conducted on a tissue section mounted on a glass slide to highlight by selective staining certain morphological indicators of disease states. Typical steps include pretreatment of the tissue section to reduce non-specific binding, antibody treatment and incubation, enzyme labeled secondary antibody treatment and incubation, substrate reaction with the enzyme to produce a fluorophore or chromophore highlighting areas of the tissue section having epitopes binding with the antibody, counterstaining, and the like. Each of these steps is separated by multiple rinse steps to remove unreacted residual reagent from the prior step. Incubations are conducted at elevated temperatures, usually around 40.degree. C., and the tissue must be continuously protected from dehydration. In situ DNA analysis relies upon the specific binding affinity of probes with unique nucleotide sequences in cell or tissue samples and similarly involves a series of process steps, with a variety of reagents and process temperature requirements.
Automated systems have been explored to introduce cost savings, uniformity of slide preparation, and reduction of procedural human errors. Stross, W. et al, J. Clin. Pathol. 42:106-112 (1989) describes a system comprising a series of baths positioned under the circumference of a circular, rotatable disc from which slide trays are suspended. The disc is lifted to lift slide trays from their baths, turned to position the slide trays above the next consecutive bath, and lowered to immerse the slide trays in the baths. This operation can be automated with suitable timers and switches. This system exposes each of the slides to the same treatment and relies on dipping for application of reactants and rinsing.
Stark, E. et al, J. Immunol. Methods. 107:89-92 (1988) describes a microprocessor controlled system including a revolving table or carousel supporting radially positioned slides. A stepper motor rotates the table, placing each slide under one of the stationary syringes positioned above the slides. A predetermined volume of liquid, determined by a dial, is delivered to a slide from each syringe. Microprocessor controls are provided.
Cosgrove, R. et. al., ACL. pp. 23-27 (December, 1989) describe an immunostaining apparatus for auto-pipetting reagents into a slide well from a Carousel holding up to 18 reagent vials. Below each well, a coverplate spaced from the surface of each slide provides cover and defines a reagent flow channel. The slides are suspended at a steep angle. Reagent from the well flows downward over the slide surface. A row of slides are suspended for sequential treatment. Washing is accomplished by a 3 to 4 minute continuous running wash over the sample, yielding an estimated 20:1 wash/reagent ratio.
Brigati, D. et al, J. Histotechnology 11:165-183 (1988) and Unger, E., Brigati, D. et al, et al, J. Histotechnology. 11:253-258 (1988) describe the Fisher automated work station using capillary gap technology. A coverplate is placed over the slide, forming a capillary gap. Liquid is introduced into the capillary gap by placing the lower edge of the plate-slide pair in a liquid. Liquid is removed by placing the lower edge of the plate-slide pair on a blotter. The system is further described in U.S. Pat. Nos. 4,777,020, 4,798,706 and 4,801,431. The previously known devices are limited in theist performance and unable to satisfy the needs for automated, high precision immunohistology.
It is an object of this invention to provide a device which provides more rapid, reliable and more reproducible results than standard methods; can perform any standard immunochemical assay including assays relying on immunofluorescence, indirect immunoassay procedures, peroxidase anti-peroxidase methods, or avidin-biotin technology; preforms all steps of the immunohistochemical assay irrespective of complexity or their order, at the time and temperature, and in the environment needed; and is cost effective in terms of equipment, reagent and labor costs.